Rapid cooling device and method for a calibration bath

ABSTRACT

A device includes a chamber having an interior surface formed from a material that reflects infrared energy. A tank is disposed within the chamber. A bottom wall of the tank is spaced apart from a bottom wall of the chamber, and side walls of the tank are spaced apart from side walls of the chamber. A conduit is formed between the bottom wall of the tank and the bottom wall of the chamber and between the side walls of the tank and the side walls of the chamber. A fan or pump moves air into the conduit past the bottom and side walls of the tank to cool a fluid disposed within the tank. A processor controls a speed at which a motor of the fan or pump rotates based on input received from one or more temperature sensors.

BACKGROUND Technical Field

The present disclosure relates to temperature regulation, and moreparticularly to regulation of the temperature of fluids used incalibration bath devices.

Description of the Related Art

Calibration baths use a volume of fluid to provide a constanttemperature environment for calibrating thermal devices, such astemperature sensors and digital thermometers, for example. Because thetemperature of the fluid is critical to accurately calibrating suchdevices, insulating materials and other means are used to reduce theimpact of ambient conditions on the temperature of the fluid.

In calibration baths, heaters can be used to increase the temperature ofa working volume of fluid to a desired temperature at which calibrationof thermal devices is to be performed. These baths are not usuallyequipped with a cooling system to decrease the temperature of theworking volume of fluid. Instead, when an operator wishes to decreasethe temperature of the working volume of fluid, the operator simplyswitches off the heat source and allows ambient conditions to removeheat from the working volume of fluid, which can take a considerableamount of time. For example, if a working volume of fluid in acalibration bath is heated to a temperature that is several degreeshigher than a desired temperature at which calibration of thermaldevices is to be performed, it can take several minutes for ambientconditions to cool the fluid to the desired temperature, depending onthe actual ambient conditions. By way of another example, it can takeseveral hours to cool a working volume of fluid from 250° C. to 35° C.using a conventional calibration bath.

Calibration baths can be portable and moved to perform calibration ofthermal devices at a variety of locations. It may be desirable toquickly cool a fluid in a portable calibration bath before moving thecalibration bath, so that it can be moved safely without the risk of hotfluid spilling and causing severe burns to an operator, for example.

High-temperature calibration baths often use silicone oils as fluidmedia. Silicone oils degrade rapidly at temperatures above theiroxidation temperature. Silicone oils are expensive. Accordingly, it maybe desirable to quickly cool such oils to a temperature that is belowtheir oxidation temperature after calibration of thermal devices isperformed, to extend the useful life of the oils.

Vapor compression refrigeration systems and external cooling fromchillers can be used to speed up cooling of working volumes of fluids inhigh-temperature calibration baths; however, vapor compressionrefrigeration systems limit the high end of a calibration bath'stemperature range due to limits of a refrigerant's temperature range,and limits of a lubricating oil that travels throughout the plumbing ofsuch systems. For example, the high end of a calibration bath'stemperature range that uses a vapor compression refrigeration system maybe limited to 170° C. In addition, compressors and refrigerants used insuch systems can be damaged when return gas temperatures aresufficiently high to damage exhaust valves therein, for example.Chillers that externally cool working volumes of fluids in calibrationbaths have the same problems.

Thermo-electric modules (TEMs) also can be used to speed up cooling ofworking volumes of fluids in calibration baths. However, TEMs may bedamaged when subjected to high temperatures and thus limit the high endof a calibration bath's temperature range.

In addition, coils through which compressed air or a liquid iscirculated have been used as accessories to speed up cooling of workingvolumes of fluids in high-temperature calibration baths. Such coils canbe expensive and dangerous. For example, if tap water is circulatedthrough such a coil, dangerously high pressures can result if thetemperature of a working volume of fluid is sufficiently high to causethe water to boil.

BRIEF SUMMARY

A device may be summarized as including a chamber having a bottom walland a plurality of side walls; a tank disposed within the chamber, thetank including a bottom wall and a plurality of side walls, the bottomwall of the tank being spaced apart from the bottom wall of the chamber,the side walls of the tank being spaced apart from the side walls of thechamber; a conduit disposed between the bottom wall of the tank and thebottom wall of the chamber and between the side walls of the tank andthe side walls of the chamber; a motor coupled to a fluid propulsiondevice, wherein the fluid propulsion device, in operation, moves airinto the conduit past the bottom wall and side walls of the tank; and aprocessor coupled to the motor, wherein the processor, in operation,controls a speed at which the motor rotates. The processor, inoperation, may control the speed at which the motor rotates by causing acontrol signal to be supplied to the motor, the control signal being apulse-width modulated signal having a maximum duty cycle that may beless than one-hundred percent.

The device may further include a memory storing instructions that, whenexecuted by the processor, cause the device to: obtain a firstindication of a current temperature of a fluid disposed within the tank;obtain an indication of a desired temperature of the fluid disposedwithin the tank; obtain a first power level value, based on the firstindication of the current temperature of the fluid and the indication ofthe desired temperature of the fluid; and generate a first controlsignal based on the first power level value, the first control signalcausing the motor to rotate at a first speed. The instructions stored bythe memory, when executed by the processor, may cause the device to:obtain a second indication of the current temperature of the fluiddisposed within the tank; obtain a second power level value, based onthe second indication of the current temperature of the fluid and theindication of the desired temperature of the fluid; and generate asecond control signal based on the second power level value, the secondcontrol signal causing the motor to rotate at a second speed, the secondspeed being different from the first speed. The first speed may begreater than the second speed, and the instructions stored by thememory, when executed by the processor, may cause the device to generatethe first control signal before generating the second control signal.

The device may further include a memory storing instructions that, whenexecuted by the processor, cause the device to: obtain an indication ofan ambient temperature; obtain an indication of a current temperature ofa fluid disposed within the tank; obtain an indication of a desiredtemperature of the fluid disposed within the tank; obtain a power levelvalue, based on the indication of the ambient temperature, theindication of the current temperature of the fluid, and the indicationof the desired temperature of the fluid; generate a control signal basedon the power level value; and provide the control signal to the motor.

The device may further include a heater circuit which, in operation,generates heat within the tank.

The device may further include one or more temperature sensors; and amemory storing instructions that, when executed by the processor, causethe processor to control the speed at which the motor rotates based oninput from the one or more temperature sensors. An interior surface ofthe chamber may reflect thermal energy incident thereon.

The device may further include a first valve disposed adjacent to aninlet of the conduit, wherein the first valve, in operation, enables airmoved by the fluid propulsion device to flow through the first valveinto the conduit and prevents air within the conduit from flowingthrough the first valve out of the conduit.

The device may further include a second valve disposed adjacent to anoutlet of the conduit, wherein the second valve, in operation, enablesthe air within the conduit to flow through the second valve out of theconduit and prevents air outside of the conduit from flowing through thesecond valve into the conduit.

A method may be summarized as including providing a chamber having abottom wall and a plurality of side walls; providing a tank within thechamber, the tank including a bottom wall and a plurality of side walls,the bottom wall of the tank being spaced apart from the bottom wall ofthe chamber, the side walls of the tank being spaced apart from the sidewalls of the chamber, and a conduit being disposed between the bottomwall of the tank and the bottom wall of the chamber and between the sidewalls of the tank and the side walls of the chamber; providing a motorcoupled to a fluid propulsion device, wherein the fluid propulsiondevice, in operation, moves air into the conduit and past the bottomwall and side walls of the tank; and coupling a processor to the motor;and controlling a speed at which the motor rotates using the processor.

The method may further include reflecting thermal energy incident on aninterior surface of the chamber toward the tank.

The method may further include obtaining a first indication of a currenttemperature of a fluid disposed within the tank; obtaining an indicationof a desired temperature of the fluid disposed within the tank;obtaining a first power level value, based on the first indication ofthe current temperature of the fluid and the indication of the desiredtemperature of the fluid; generating a first control signal based on thefirst power level value; and providing the first control signal to themotor, the first control signal causing the motor to rotate at a firstspeed.

The method may further include obtaining a second indication of thecurrent temperature of the fluid disposed within the tank; obtaining asecond power level value based on the second indication of the currenttemperature of the fluid and the indication of the desired temperatureof the fluid; generating a second control signal based on the secondpower level value; and providing the second control signal to the motor,the second control signal causing the moto to rotate at a second speed,the second speed being different from the first speed. The first speedmay be greater than the second speed, and the first control signal maybe generated before the second control signal is generated.

The method may further include obtaining an indication of an ambienttemperature; obtaining an indication of a current temperature of a fluiddisposed within the tank; obtaining an indication of a desiredtemperature of the fluid disposed within the tank; obtaining a powerlevel value, based on the indication of the ambient temperature, theindication of the current temperature of the fluid, and the indicationof the desired temperature of the fluid; generating a control signalbased on the first power level value; and providing the control signalto the motor.

The method may further include generating heat within the tank beforeproviding the first control signal to the motor.

The method may further include providing a first valve adjacent to aninlet of the conduit; enabling air moved by the fluid propulsion deviceto flow through the first valve into the conduit; preventing air withinthe conduit from flowing through the first valve out of the conduit.

The method may further include providing a second valve adjacent to anoutlet of the conduit; enabling the air within the conduit to flowthrough the second valve out of the conduit; and preventing air outsideof the conduit from flowing through the second valve into the conduit.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram of a calibration device, according to one ormore embodiments of the present disclosure.

FIG. 2 is an isometric view of a calibration device, according to one ormore embodiments of the present disclosure.

FIG. 3 is a sectional view of a calibration device, according to one ormore embodiments of the present disclosure.

FIG. 4 is a side view of a calibration device, according to one or moreembodiments of the present disclosure.

FIG. 5 is a sectional view of a calibration device, according to one ormore embodiments of the present disclosure.

FIG. 6 is a flowchart of a method, according to one or more embodimentsof the present disclosure.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a calibration device 100, according to oneor more embodiments of the present disclosure. The calibration device100 includes a microprocessor 102 having a memory 104 and a processor106. The calibration device 100 also includes a memory 108 that iscoupled to the microprocessor 102. In one or more embodiments, thememory 104 is comprised of one or more conventional Random Access Memory(RAM) modules. In one or more embodiments, the memory 108 is comprisedof one or more conventional Electronically Erasable Programmable ReadOnly Memory (EEPROM) modules. As will be explained in detail below, thememory 108 stores instructions that, when executed by the processor 106,cause the calibration device 100 to perform the functions describedbelow. In one or more embodiments, the processor 106 uses the memory 104as a working memory as the processor 106 executes the instructions thatare stored by the memory 108.

The calibration device 100 also includes input/output (I/O) circuitry110. In one or more embodiments, the I/O circuitry 110 includes inputdevices such as a touch input device, buttons, knobs, and/or dials, forexample, that an operator can use to control operation of thecalibration device 100. Additionally, in one or more embodiments, theI/O circuitry 110 includes one or more output devices such as a displaydevice (e.g., liquid crystal display), light emitting devices, speakers,a buzzer, and/or data interfaces (e.g., Universal Serial Bus (USB)interfaces), for example.

The calibration device 100 also includes a fan motor driver circuit 112that is electrically coupled to a fan motor 114 and the microprocessor102. The microprocessor 102 controls a speed at which the fan motor 114rotates by providing a control signal 116 to the fan motor drivercircuit 112, which provides a corresponding control signal 118 to thefan motor 114. In one or more embodiments, the control signals 116 and118 are pulse width modulated power signals that cause the fan motor 114to operate at a variety of speeds, depending on a duty cycle of thecontrol signal 116 and a duty cycle of the control signal 118. The dutycycle of each of the control signals 116 and 118 is a ratio of “on” timeto a predetermined period of time corresponding to one cycle. In one ormore embodiments, the microprocessor 102 generates the control signal116 based on an amount of cooling required, in accordance with a programstored by the memory 108. In one or more embodiments, the fan motordriver circuit 112 generates the control signal 118 by amplifying thecontrol signal 116 to provide higher current and voltage that isrequired by the fan motor 114. In one or more embodiments, the controlsignals 116 and 118 have the same duty cycle. In one or moreembodiments, the fan motor 114 provides to the microprocessor 102 asignal 120 indicating the actual speed at which the fan motor 114 isrotating.

The calibration device 100 also includes a heater circuit 122 and one ormore temperature sensors 124. In one or more embodiments, the heatercircuit 122 includes one or more heating elements attached to outersurfaces of sides walls 156 of a tank 160. In one or more embodiments,the heater circuit 122 includes a coil immersion heater. For example,the heater circuit 122 includes one or more resistive heating elementsthat produce heat in response to a current flowing therethrough. Theheat from the heating elements is transferred to a first fluid that iscirculated within a coil. The coil is disposed within the tank 160 neara propeller 172, for example, above the propeller 172 (see FIG. 3). Thepropeller 172 circulates a second fluid that has been heated by the coilto maintain the second fluid at a constant temperature that is uniformlydistributed throughout the tank 160.

The microprocessor 102 provides a control signal to the heater circuit122 based on a signal received from the one or more temperature sensors124.

For example, if the memory 104 of the microprocessor 102 storesinformation indicating that a desired temperature is 250° C. and themicroprocessor 102 receives from a temperature sensor 124 a signalindicating that a temperature sensed by the temperature sensor 124 is225° C., the microprocessor 102 provides a control signal to the heatercircuit 122 that causes the heater circuit 122 to produce a relativelyhigh amount of heat. Subsequently, if the microprocessor 102 receivesfrom a temperature sensor 124 a signal indicating that a temperaturesensed by the temperature sensor 124 is 255° F., the microprocessor 102provides a control signal to the heater circuit 122 that causes theheater circuit 122 to produce less heat, or no heat.

In one or more embodiments, the microprocessor 102 controls the fanmotor 114 based on a state of the heater circuit 122 and/or a sensedtemperature of the fluid in the tank 160. For example, while themicroprocessor 102 controls the heater circuit 122 to be in a state inwhich it generates a relatively high amount of heat, the microprocessor102 controls the fan motor 114 to be in an off state. Once a fluidwithin the tank 160 is heated to a desired temperature by the heatercircuit 122, the microprocessor 102 controls the heater circuit 122 tobe in a state in which it generates less heat. If a current temperatureof the fluid within the tank 160 is greater than a desired temperatureby a first predetermined amount, the microprocessor 102 controls the fanmotor 114 to rotate at a relatively high rate. As the temperature of thefluid within the tank 160 gets closer to the desired temperature, themicroprocessor 102 controls the fan motor 114 to rotate at a lower rate.When the current temperature of the fluid within the tank 160 is greaterthan the desired temperature by a second predetermined amount, which issmaller than the first predetermined amount, the microprocessor 102controls the fan motor 114 to be in an off state.

In one or more embodiments, the memory 108 stores a table or othersuitable data structure in which a plurality of values of the differencebetween the current temperature and the desired temperature of the fluidwithin the tank 160 is associated with a plurality of correspondingvalues of the speed of the fan motor 114. Alternatively, the memory 108may store a formula-driven algorithm that dynamically calculates adesired speed of the fan motor 114 based on a determined differencebetween the current temperature and the desired temperature of the fluidwithin the tank 160. It is noted that the speed at which the fan motor114 rotates, in this embodiment, is proportional to the power level ofthe control signal supplied thereto. For example, while a signal havinga power level corresponding to a maximum power level that can besupplied to the fan motor 114 (e.g., a signal having duty cycle of100%), the fan motor 114 may rotate at 3000 revolutions per minute.Similarly, while a signal having a power level corresponding to half ofthe maximum power level (e.g., a signal having duty cycle of 50%) thatcan be supplied to the fan motor 114, the fan motor 114 may rotate at1500 revolutions per minute. In one or more embodiments, the memory 108stores instructions that cause the microprocessor 102 convert a value ofthe speed of the fan motor 114 obtained from such a table or datastructure or algorithm into a corresponding power level value. In one ormore embodiments, the memory 108 stores a table or other suitable datastructure in which a plurality of values of the difference between thecurrent temperature and the desired temperature of the fluid within thetank 160 is associated with a plurality of power level values for thecontrol signal provided to the fan motor 114. Alternatively, the memory108 may store an algorithm that dynamically calculates a power levelvalue for driving the fan motor 114 based on a determined differencebetween the current temperature and the desired temperature of the fluidwithin the tank 160.

The calibration device 100 also includes a stir motor driver circuit 126that is electrically coupled to a stir motor 128 and the microprocessor102. In one or more embodiments, the stir motor driver circuit 126manages power control and commutation for the stir motor 128. In one ormore embodiments, commutation is synchronized with the angular positionof the stir motor 128 as it rotates by utilizing feedback to the stirmotor driver circuit 126 provided from Hall-effect sensors included inthe stir motor 128. In one or more embodiments, the stir motor 128 is abrushless direct current (DC) motor.

The speed of the stir motor 128 is determined by the voltage supplied tothe stir motor 128. The microprocessor 102 controls the speed at whichthe stir motor 128 rotates by providing a control signal 130 to the stirmotor driver circuit 126, which provides a corresponding control signal132 to the stir motor 128. In one or more embodiments, the controlsignals 130 and 132 are pulse width modulated power signals that causethe stir motor 128 to operate at a variety of speeds, depending on aduty cycle of the control signal 130 and a duty cycle of the controlsignal 132. The duty cycle of each of the control signals 130 and 132 isa ratio of “on” time to a predetermined period of time corresponding toone cycle. In one or more embodiments, the microprocessor 102 generatesthe control signal 130 in accordance with a program stored by the memory108. In one or more embodiments, the stir motor driver circuit 126generates the control signal 132 by amplifying the control signal 130.In one or more embodiments, the control signals 130 and 132 have thesame duty cycle. In one or more embodiments, the stir motor 128 providesto the microprocessor 102 a signal 134 indicating the actual speed atwhich the stir motor 128 is rotating.

In one or more embodiments, the calibration device 100 includes avibration sensor 136, for example, an accelerometer. The vibrationsensor 136 produces a signal that indicates a level of vibration sensedby the vibration sensor 136, which is provided to the microprocessor102. After receiving the signal, the microprocessor 102 compares thelevel of vibration sensed by the vibration sensor 136 to a predeterminedthreshold value. If the level of vibration sensed by the vibrationsensor 136 is greater than or equal to the threshold value, themicroprocessor 102 can cause a light emitting diode (LED) included inthe I/O circuitry 110 to emit light, cause a speaker included in the I/Ocircuitry 110 to emit sound, cause the speed at which the fan motor 114rotates to decrease, and/or cause the speed at which the stir motor 128rotates to decrease, for example.

FIG. 2 is an isometric view of the calibration device 100, according toone or more embodiments of the present disclosure. The calibrationdevice 100 includes a control panel 140, which includes one or more ofthe components of the I/O circuitry 110 discussed above. For example,the control panel 140 includes a plurality of buttons that an operatoruses to input parameters, which the microprocessor 102 uses to controloperation of the calibration device 100.

The calibration device 100 includes a case that has a front panel 142with a plurality of apertures 144 formed therein. As will be explainedbelow, ambient air enters the calibration device 100 through theapertures 144 formed in the front panel 142 and cools a fluid disposedwithin the tank 160 that is used during calibration of thermal devices.The tank 160 includes a flange 146 to which a tank cover 148 can beattached using a plurality of bolts 150, for example.

FIG. 3 is a sectional view of the calibration device 100 taken along theline 3-3 shown in FIG. 2, according to one or more embodiments of thepresent disclosure. Components of the calibration device 100 that arenot necessary to explain aspects of the calibration device 100 discussedbelow are not shown in FIG. 3 to simplify the discussion that follows.

A chamber 152 is disposed within the calibration device 100. The chamber152 includes a bottom wall 154 and a plurality of side walls 156 thatextend from the bottom wall 154. An interior surface of the bottom wall154 and each of the side walls 156 reflect thermal energy (e.g.,infrared energy) from the tank 160 that is incident thereon. The tank160 is disposed within the chamber 152. In one or more embodiments,interior surfaces of the bottom wall 154 and each of the side walls 156are formed from stainless steel, which reflects a majority of thermalenergy that is emitted from the tank 160 back toward the tank 160.

An insulating material 158 is disposed outside of the chamber 152surrounding an exterior surface of the bottom wall 154 and each of theside walls 156. The insulating material 158 reduces the amount ofthermal energy (e.g., heat) that is transferred between the chamber 152and an ambient environment in which the calibration device 100 islocated. In one or more embodiments, the insulating material 158comprises a ceramic fiber blanket.

The tank 160 includes a bottom wall 162 and four side walls 164 a, 164b, 164 c, and 164 d, which extend from the bottom wall 162. As describedin detail below, one or more of the side walls 164 a-164 d include oneor more sloped surfaces that are arranged to efficiently disperse afluid, which was recently heated by the heater circuit 122 and propelledby the propeller 172, so that the recently heated fluid rapidly mixes inthe tank 160 and the fluid is maintained at a constant temperaturethroughout the tank 160.

In one or more embodiments, a first side wall 164 a includes a firstsurface 166 a that extends from a surface 162 a of the bottom wall 162,and a second surface 166 b that extends from the first surface 166 a. Asecond side wall 164 b includes a first surface 166 c that extends fromthe surface 162 a of the bottom wall 162, and a second surface 166 dthat extends from the first surface 166 c. The first side wall 164 a isopposite the second side wall 164 b.

In one or more embodiments, the first surface 166 a of the first sidewall 164 a is longer than the first surface 166 c of the second sidewall 164 b, and the second surface 166 d of the second side wall 164 bis longer than the second surface 166 b of the first side wall 164 a.For example, a distance measured along the first surface 166 a from thetop of the first surface 166 a to the bottom of the first surface 166 ais greater than a distance measured along the first surface 166 c fromthe top of the first surface 166 c to the bottom of the first surface166 c, and a distance measured along the second surface 166 d from thetop of the second surface 166 d to the bottom of the second surface 166d is greater than a distance measured along the second surface 166 bfrom the top of the second surface 166 b to the bottom of the secondsurface 166 b.

In one or more embodiments, the first surface 166 a of the first sidewall 164 a and the surface 162 a of the bottom wall 162 form an obtuseangle A within the tank 160; the first surface 166 a and the secondsurface 166 b of the first side wall 164 a form an obtuse angle B withinthe tank 160; the first surface 166 c of the second side wall 164 b andthe surface 162 a of the bottom wall 162 form an obtuse angle C withinthe tank 160; and the first surface 166 c and the second surface 166 dof the second side wall 164 b form an obtuse angle D within the tank160. In one or more embodiments, the angle A is 135°, the angle B is135°, the angle C is 130°, and the angle D is 140°. The angles A, B, C,and D can have other values without departing from the scope of thepresent disclosure.

While the heater circuit 122 is heating a fluid disposed in the tank160, some of the fluid that was recently heated by the heater circuit122 is moved downwardly by the propeller 172 toward the first surface166 a of the first side wall 164 a. Some of the recently heated fluiddeflects off of the first surface 166 a of the first side wall 164 a andmoves upwardly across the tank 160 away from the first surface 166 a ofthe first side wall 164 a. Some of the recently heated fluid travelsacross a lower portion of the tank 160 and deflects off of the firstsurface 166 c of the second side wall 164 b, which causes the fluid tomove upwardly across the tank 160 away from the first surface 166 c ofthe second side wall 164 b. The arrangement of the first surface 166 aof the first side wall 164 a and the first surface 166 c of the secondside wall 164 b with respect to each other, and with respect to thesurface 162 a of the bottom wall 162 and the propeller 172, causes therecently heated fluid to rapidly disperse within the tank 160.

In one or more embodiments, the tank 160 includes rounded features thatenable the propeller 172 to efficiently circulate a fluid within thetank 160. Such rounded features prevent the fluid within the tank 160from being trapped or impeded as the propeller 172 moves the fluidtoward the first surface 166 a of the first side wall 164 a and thefirst surface 166 c of the second side wall 164 b, which causes thefluid to move upwardly and disperse throughout the tank 160, asdescribed above. Examples of such rounded features are discussed ingreater detail below with reference to FIG. 5.

In one or more embodiments, the bottom wall 162 and side walls 164 a-164d are formed from stainless steel. In one or more embodiments, thebottom wall 162 and side walls 164 a-164 d are integrally formed. In oneor more embodiments, the bottom wall 162 and side walls 164 a-164 d arewelded together. In one or more embodiments, a drainage conduit 168 isfluidly coupled to the first surface 166 c of the second side wall 164b, which enables a fluid to be drained from the tank 160. In one or moreembodiments, each of the surfaces 164 a-164 d and the surface 162 a isflat.

A fluid (e.g., silicone oil) can be placed in the tank 160 via anopening that is accessible while the tank cover 148 is removed. Thefluid is then heated to and maintained at a desired temperature.Subsequently, one or more thermal devices are placed in the fluid thatis disposed in the tank 160 via the opening, and calibration of thethermal devices is performed. The stir motor 128 is operated to helpensure that the temperature of a fluid disposed in the tank 160 ismaintained at a constant temperature that is uniformly distributedthroughout the tank 160 while calibration of the thermal devices isperformed.

The stir motor 128 is coupled to a fluid propulsion device that causes afluid within the tank 160 to be circulated. In one or more embodiments,the fluid propulsion device is the propeller 172. A shaft 170 couplesthe propeller 172 to a rotor (not shown) of the stir motor 128.Accordingly, the propeller 172 rotates while the rotor of the stir motor128 rotates. The propeller 172 includes a plurality of blades 174 thatare angled to move the fluid toward the first surface 166 a of the firstside wall 164 a while the propeller 172 rotates in a predetermineddirection (e.g., clockwise). A guard 176 having a plurality of aperturesformed therein is disposed within the tank 160 adjacent to the propeller172. The guard 176 prevents a thermal device from coming into contactwith the propeller 172 while the device is being calibrated within thetank 160.

In one or more embodiments, the fluid propulsion device is an impellerthat is disposed within a pump. The impeller is coupled to the stirmotor 128. Rotation of the stir motor 128 causes the impeller to rotatethereby creating a pressure differential within the pump, which causes afluid within the tank 160 to be drawn into an inlet of the pump and thenforced out of an outlet of the pump. The pump is arranged so that fluidexiting the outlet is heated by the heater circuit 122. Additionally,fluid exiting the outlet of the pump is directed toward the firstsurface 166 a of the first side wall 164 a, in a manner that is similarto embodiments in which the propeller 172 directs the fluid toward thefirst surface 166 a of the first side wall 164 a.

In one or more embodiments, the fluid propulsion device is a piston,plunger, or diaphragm that is disposed within a pump. The piston,plunger, or diaphragm is coupled to the stir motor 128. Rotation of thestir motor 128 causes the piston, plunger, or diaphragm to reciprocate(e.g., move in a first direction and then in a second direction, whereinthe first direction is opposite the second direction) within a chamberthereby creating a pressure differential within the pump, which causes afluid within the tank 160 to be drawn into an inlet of the pump and thenforced out of an outlet of the pump. The pump is arranged so that fluidexiting the outlet is heated by the heater circuit 122. Additionally,fluid exiting the outlet of the pump is directed toward the firstsurface 166 a of the first side wall 164 a, in a manner that is similarto embodiments in which the propeller 172 directs the fluid toward thefirst surface 166 a of the first side wall 164 a.

It may be desirable to lower the temperature of the fluid disposed inthe tank 160 before, during, and after calibration testing. For example,while the stir motor 128 is operated, friction between the propeller 172and the fluid may cause the temperature of the fluid within to riseabove a desired temperature at which a thermal device is to becalibrated. The calibration device 100 is arranged so that the fluidwithin the tank 160 can be cooled quickly, if necessary, and maintainedat a constant temperature.

More particularly, the tank 160 is spaced apart from the chamber 152. Aconduit 178 is formed between the tank 160 and the chamber 152. Theconduit 178 extends between the bottom wall 154 of the chamber 152 andthe bottom wall 162 of the tank 160, and between the side walls 156 ofthe chamber 152 and respective side walls 164 a-164 c of the tank 160.The conduit 178 includes an inlet 180 and an outlet 182, which aredisposed in a lower portion of the chamber 152 to help prevent naturalconvection of air within the conduit 178.

A valve 184 is disposed adjacent to the inlet 180. In one or moreembodiments, a valve 186 is disposed adjacent to the outlet 182. In oneor more embodiments, the valve 184 and the valve 186 are check valvesthat enable air to pass therethrough in only one direction. Moreparticularly, the valve 184 enables air to pass only into the inlet 180of the conduit 178, and the valve 186 enables air to pass only out ofthe outlet 182 of the conduit 178. Some embodiments may have only onevalve, e.g., the valve 184 disposed adjacent to the inlet 180. In one ormore embodiments, the conduit 178 exposes the entire external surface ofthe tank 160 to air that flows through the conduit 178.

A fan 188 is disposed within the calibration device 100 adjacent to thechamber 152. The fan 188 includes the fan motor 114 and a propeller 190having a plurality of blades 192. A rotor (not shown) of the fan motor114 is coupled to the propeller 190. Accordingly, the propeller 190rotates while the fan motor 114 rotates. The blades 192 are angled suchthat, while the propeller 190 rotates in a predetermined direction(e.g., clockwise), the propeller 190 draws ambient air through apertures144 formed in the front panel 142 and directs the ambient air throughthe valve 184 into the inlet 180 of the conduit 178. The fan 188provides a relatively high-pressure air flow into the conduit 178. Inone or more embodiments, the ambient air travels through the conduit 178around the tank 160, exits through the outlet 182, passes through thevalve 186, and continues out of the calibration device 100 throughapertures formed in a back panel of the case of the calibration device100.

As the ambient air passes over the bottom wall 162 and the side walls164 a-164 d of the tank 160, the ambient air is heated by the hightemperature fluid in the tank 160. Subsequently, the propeller 190forces the heated air out of the calibration device 100. Accordingly,while the fan motor 114 rotates, a fluid disposed in the tank 160 iscooled by the flow of ambient air passing over the bottom wall 162 andthe side walls 164 a-164 d of the tank 160.

FIG. 4 is a side plan view of the calibration device 100, according toone or more embodiments of the present disclosure. FIG. 5 is a sectionalview of the calibration device 100 taken along the line 5-5 in FIG. 4,according to one or more embodiments of the present disclosure.Components of the calibration device 100 that are not necessary toexplain aspects of the calibration device 100 discussed below are notshown in FIG. 5 to simplify the discussion that follows.

As shown in FIG. 5, the conduit 178 extends around the side walls 164a-164 d of the tank 160, between the side walls 164 a-164 d of the tank160 and the side walls 156 of the chamber 152. Accordingly, air flowingin the conduit 178 contacts a large surface area on the exterior surfaceof the tank 160, which enables the air to rapidly remove heat from thefluid within the tank 160.

In one or more embodiments, the tank 160 includes four rounded surfaces194, three of which are shown in FIG. 5. More particularly, the bottomwall 162 has a rectangular shape. Each rounded surface 194 is formedbetween one of the four sides of the bottom wall 162 and the bottom ofone of the side walls 164 a-164 d. In one or more embodiments, eachrounded surface 194 has the shape of an elliptical or circular arc witha radius of 5 millimeters. In one or more embodiments, each roundedsurface 194 has the shape of an elliptical or circular arc with a radiusof 10 millimeters. Each rounded surface 194 can have a radius of adifferent length or of a different round shape without departing fromthe scope of the present disclosure. The rounded surfaces 194 preventthe fluid in the tank 160 from becoming trapped in the lower portions ofthe tank 160 where the side walls 164 a-164 d meet the bottom wall 162,as the fluid is being circulated by the propeller 172.

In one or more embodiments, the tank 160 includes four rounded corners196, two of which are shown in FIG. 5. Each rounded corner 196 is formedat one of the four lower corners of the tank 160 where the bottom wall162 and two adjacent side walls 164 a-164 d meet. In one or moreembodiments, each rounded corner 196 has the shape of a portion of anellipsoid or spherical surface with a radius of 5 millimeters. In one ormore embodiments, each rounded corner 196 has the shape of a portion ofan ellipsoid or spherical surface with a radius of 10 millimeters. Eachrounded corner 196 can have a radius of a different length or of adifferent round shape without departing from the scope of the presentdisclosure. The rounded corners 196 prevent the fluid in the tank 160from becoming trapped in the lower corners of the tank 160, where pairsof adjacent side walls 164 a-164 d meet the bottom wall 162, as thefluid is being circulated by the propeller 172. The rounded surfaces 194and the rounded corners 196 enable the fluid to circulate within thetank 160 more efficiently than in conventional tanks that do not includesuch rounded features.

FIG. 6 is a flowchart of a method 200 of operating the calibrationdevice 100, according to one or more embodiments of the presentdisclosure. The method begins at 202, for example, when an operatorplaces the calibration device 100 in a mode for configuring parametersfor performing calibration testing. The method 200 then proceeds to 204.

At 204, an indication of an ambient temperature is obtained. The ambienttemperature is a temperature in the environment in which the calibrationdevice 100 is located. In one or more embodiments, the microprocessor102 receives the indication of the ambient temperature in response to anoperator actuating one or more buttons of a keypad of the control panel140 to enter the ambient temperature, or in response to the operatorselecting the ambient temperature within a list of predeterminedtemperatures included in a menu. In one or more embodiments, themicroprocessor 102 receives the indication of the ambient temperaturefrom one of the temperature sensors 124. The method 200 then proceeds to206.

At 206, an indication of a desired temperature is obtained. The desiredtemperature is a temperature at which a fluid in the tank 160 is to beheated and maintained. For example, the microprocessor 102 receives theindication of the desired temperature in response to an operatoractuating one or more buttons of a keypad of the control panel 140 toenter the desired temperature, or in response to the operator selectingthe desired temperature within a list of predetermined temperaturesincluded in a menu. The method 200 then proceeds to 208.

At 208, an indication of a current temperature is obtained. The currenttemperature is a current temperature of the fluid in the tank 160. Forexample, the microprocessor 102 receives the indication of the currenttemperature from one or more of the temperature sensors 124. The method200 then proceeds to 210.

At 210, a power level value is obtained. The power level value is aparameter associated with the control signal 118 that is provided to thefan motor 114. In one or more embodiments, the microprocessor 102executes instructions stored in the memory 108 to obtain the power levelvalue based on the indications of the desired temperature and thecurrent temperature obtained at 206 and 208, respectively. For example,the memory 108 stores a table or other suitable data structure thatassociates a plurality of values of differences between the currenttemperature and the desired temperature of the fluid in the tank 160with a plurality of corresponding power level values. The microprocessor102 calculates the difference between the current temperature and thedesired temperature of the fluid in the tank 160 based on theindications obtained at 206 and 208, respectively. The microprocessor102 then obtains a power level value that is associated with a value ofthe difference between the current temperature and the desiredtemperature of the fluid in the tank 160 that most closely matches thecalculated difference between the current temperature and the desiredtemperature of the fluid in the tank 160.

In one or more embodiments, the microprocessor 102 takes the ambienttemperature of the environment in which the calibration device 100 islocated into consideration when obtaining the power level value at 210.For example, the memory 108 stores a plurality of tables or othersuitable data structures that associate a plurality of values ofdifferences between the current temperature and the desired temperatureof the fluid in the tank 160 with a plurality of corresponding powerlevel values, wherein each table is associated with a different value ofa difference between the temperature of the fluid in the tank 160 andthe ambient temperature. In one or more embodiments, the values includedin such tables are obtained through experimentation in view of thefollowing equation.

Q=K×A×ΔT   (Equation 1)

In equation 1, the parameter Q is the cooling energy required toestablish a desired temperature balance and thermal response using thecalibration device 100. The parameter K is the thermal conductivity tothe ambient environment in which the calibration device 100 is locatedrelative to heat loss or cooling. The parameter ΔT is the temperaturedifference between the fluid in the tank 160 and the ambientenvironment. The parameter A is the area of heat exchange. Thecalibration device 100 is constructed such that K is ΔT variable so thatthere is sufficient isolation to the ambient environment for goodcontrol and for safety while providing a higher degree of heat loss whenneeded.

In one or more embodiments, the microprocessor 102 executes instructionsstored in the memory 108 to obtain the power level value based on theindications of the ambient temperature, the desired temperature, and thecurrent temperature obtained at 204, 206, and 208, respectively. Morespecifically, the microprocessor 102 calculates the difference betweenthe current temperature of the fluid in the tank 160 and the ambienttemperature based on the indications of the ambient temperature and thecurrent temperature obtained at 204 and 206, respectively. Themicroprocessor 102 also calculates the difference between the currenttemperature of the fluid in the tank 160 and the desired temperature ofthe fluid in the tank 160 based on the indications obtained at 206 and208, respectively. In addition, the microprocessor 102 selects a tableor data structure that is associated with a value of the differencebetween the current temperature of the fluid in the tank 160 and theambient temperature that most closely matches the calculated differencebetween the current temperature of the fluid in the tank 160 and theambient temperature. The microprocessor 102 then obtains, from theselected table or data structure, a power level value that is associatedwith a value of the difference between the current temperature and thedesired temperature of the fluid in the tank 160 that most closelymatches the calculated difference between the current temperature andthe desired temperature of the fluid in the tank 160.

In one or more embodiments, the power level values included in theabove-described tables or data structures are duty cycle values of thecontrol signal 118 that is supplied to the fan motor 114. In one or moreembodiments, the maximum duty cycle value included in such a table ordata structure is less than 100%, for example, 75%. When the controlsignal 118 that is supplied to the fan motor 114 has a duty cycle thatis higher than the maximum duty cycle value, portions of fluid nearwalls of the tank 160 may become cooled too quickly. As a result, thepropeller 172 may not be able to stir the fluid in the tank 160 fastenough to ensure that the fluid has a uniform temperature throughout thevolume of fluid, which is undesirable while calibration of thermaldevices is being performed.

In one or more embodiments, the memory 108 stores tables or othersuitable data structures that are similar those described above exceptthat, instead of storing power level values, the tables or datastructures store values of speeds of the fan motor 114. In one or moreembodiments, after a speed of the fan motor 114 is obtained from one ofthose tables or data structures, the microprocessor 102 uses apredefined formula or table to convert the obtained speed into a powerlevel value that causes the fan motor 114 to rotate at the obtainedspeed.

After the power level value is obtained at 210, the method 200 proceedsto 212. At 212, a control signal is generated. For example, themicroprocessor 102 generates a control signal 116 having a duty cyclecorresponding to the power level value obtained at 210, and supplies thecontrol signal 116 to the fan motor driver circuit 112. The fan motordriver circuit 112 generates a corresponding control signal 118 based onthe control signal 116, for example, by amplifying the control signal116. The method 200 then proceeds to 214.

At 214, the control signal is supplied to a motor. For example, the fanmotor driver circuit 112 supplies the control signal 118 to the fanmotor 114. The method 200 then proceeds to 216.

At 216, a determination is made regarding whether an interrupt has beengenerated. For example, the microprocessor 102 checks the value of apredetermined variable or a voltage level of a predetermined terminaland determines whether the value of the variable or the voltage level ofthe terminal has a predetermined value. The interrupt may be generatedwhen an operator manipulates one or more buttons on the control panel140 to initiate a procedure for shutting down the calibration device100, for example. If a determination is made at 216 that an interrupthas not been generated, the method 200 returns to 204, and the acts204-216 are repeated. If a determination is made at 216 that aninterrupt has been generated, the method 200 proceeds to 218, where themethod 200 ends.

The calibration device 100 performing the method 200 provides animprovement over conventional calibration baths. For example, in oneexperiment, a fluid was heated to 250° C. using a conventionalcalibration bath and also using a calibration device according to thepresent disclosure, and the amount of time required to cool the fluid to35° C. was measured for each. The conventional calibration bath tookover 9 hours to cool the fluid to 35° C.; however, the calibrationdevice according to the present disclosure took only 45 minutes. Thus,the calibration device 100 according to the present disclosure canimprove calibration time efficiency by reducing the amount of time anoperator must wait before being able to safely move the calibrationdevice 100 after calibration of thermal devices has been performed, forexample.

In addition, the calibration device 100 performing the method 200 canextend the useful life of fluids used in the calibration device 100because the fluids do not remain heated above their oxidationtemperatures for long periods of time after calibration of thermaldevices has been performed using those fluids.

Because fluids used in the calibration device 100 can be expensive,extending the useful life of such fluids can result in significant costsavings over time. In addition, the calibration device 100 performingthe method 200 can operate at just 5° C. above ambient, for example,which cannot be accomplished with conventional calibration baths.

The various embodiments described above can be combined to providefurther embodiments. Although the example embodiments have beendescribed in the context of a high-temperature calibration bath, thepresent disclosure is applicable to low-temperature calibration baths.For example, the heater circuit 122 can be replaced with a circuit thatcools a fluid disposed within the tank 160, and the microprocessor 102can control the fan 188 to move ambient air into the conduit 178 to addheat to the fluid disposed within the tank 160. In addition, the fan 188may be replaced by a pump having a motor that is coupled to an impeller,one or more pistons, one or more plungers, or one or more diaphragms.Additionally, the microprocessor 102 may control a speed at which thepump motor rotates based input received from one or more of thetemperature sensors 124, in a manner that is similar to theabove-described manner in which the microprocessor 102 controls a speedat which the fan motor 114 rotates.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A device, comprising: a chamber including a bottom wall and aplurality of side walls; a tank disposed within the chamber, the tankincluding a bottom wall and a plurality of side walls, the bottom wallof the tank being spaced apart from the bottom wall of the chamber, theside walls of the tank being spaced apart from the side walls of thechamber; a conduit disposed between the bottom wall of the tank and thebottom wall of the chamber and between the side walls of the tank andthe side walls of the chamber; a motor coupled to a fluid propulsiondevice, wherein the fluid propulsion device, in operation, moves airinto the conduit past the bottom wall and side walls of the tank; and aprocessor coupled to the motor, wherein the processor, in operation,controls a speed at which the motor rotates.
 2. The device of claim 1,wherein the processor, in operation, controls the speed at which themotor rotates by causing a control signal to be supplied to the motor,the control signal being a pulse-width modulated signal having a maximumduty cycle that is less than one-hundred percent.
 3. The device of claim1, further comprising: a memory storing instructions that, when executedby the processor, cause the device to: obtain a first indication of acurrent temperature of a fluid disposed within the tank; obtain anindication of a desired temperature of the fluid disposed within thetank; obtain a first power level value, based on the first indication ofthe current temperature of the fluid and the indication of the desiredtemperature of the fluid; and generate a first control signal based onthe first power level value, the first control signal causing the motorto rotate at a first speed.
 4. The device of claim 3, wherein theinstructions stored by the memory, when executed by the processor, causethe device to: obtain a second indication of the current temperature ofthe fluid disposed within the tank; obtain a second power level value,based on the second indication of the current temperature of the fluidand the indication of the desired temperature of the fluid; and generatea second control signal based on the second power level value, thesecond control signal causing the motor to rotate at a second speed, thesecond speed being different from the first speed.
 5. The device ofclaim 4, wherein the first speed is greater than the second speed, andthe instructions stored by the memory, when executed by the processor,cause the device to generate the first control signal before generatingthe second control signal.
 6. The device of claim 1, further comprising:a memory storing instructions that, when executed by the processor,cause the device to: obtain an indication of an ambient temperature;obtain an indication of a current temperature of a fluid disposed withinthe tank; obtain an indication of a desired temperature of the fluiddisposed within the tank; obtain a power level value, based on theindication of the ambient temperature, the indication of the currenttemperature of the fluid, and the indication of the desired temperatureof the fluid; generate a control signal based on the power level value;and provide the control signal to the motor.
 7. The device of claim 1,further comprising: a heater circuit which, in operation, generates heatwithin the tank.
 8. The device of claim 1, further comprising: one ormore temperature sensors; and a memory storing instructions that, whenexecuted by the processor, cause the processor to control the speed atwhich the motor rotates based on input from the one or more temperaturesensors.
 9. The device of claim 1, wherein an interior surface of thechamber reflects thermal energy incident thereon.
 10. The device ofclaim 1, further comprising: a first valve disposed adjacent to an inletof the conduit, wherein the first valve, in operation, enables air movedby the fluid propulsion device to flow through the first valve into theconduit and prevents air within the conduit from flowing through thefirst valve out of the conduit.
 11. The device of claim 10, furthercomprising: a second valve disposed adjacent to an outlet of theconduit, wherein the second valve, in operation, enables the air withinthe conduit to flow through the second valve out of the conduit andprevents air outside of the conduit from flowing through the secondvalve into the conduit.
 12. A method, comprising: providing a chamberincluding a bottom wall and a plurality of side walls; providing a tankwithin the chamber, the tank including a bottom wall and a plurality ofside walls, the bottom wall of the tank being spaced apart from thebottom wall of the chamber, the side walls of the tank being spacedapart from the side walls of the chamber, and a conduit being disposedbetween the bottom wall of the tank and the bottom wall of the chamberand between the side walls of the tank and the side walls of thechamber; providing a motor coupled to a fluid propulsion device, whereinthe fluid propulsion device, in operation, moves air into the conduitand past the bottom wall and side walls of the tank; and coupling aprocessor to the motor; and controlling a speed at which the motorrotates using the processor.
 13. The method of claim 12, furthercomprising: reflecting thermal energy incident on an interior surface ofthe chamber toward the tank.
 14. The method of claim 12, furthercomprising: obtaining a first indication of a current temperature of afluid disposed within the tank; obtaining an indication of a desiredtemperature of the fluid disposed within the tank; obtaining a firstpower level value, based on the first indication of the currenttemperature of the fluid and the indication of the desired temperatureof the fluid; generating a first control signal based on the first powerlevel value; and providing the first control signal to the motor, thefirst control signal causing the motor to rotate at a first speed. 15.The method of claim 14, further comprising: obtaining a secondindication of the current temperature of the fluid disposed within thetank; obtaining a second power level value based on the secondindication of the current temperature of the fluid and the indication ofthe desired temperature of the fluid; generating a second control signalbased on the second power level value; and providing the second controlsignal to the motor, the second control signal causing the moto torotate at a second speed, the second speed being different from thefirst speed.
 16. The method of claim 15, wherein the first speed isgreater than the second speed, and the first control signal is generatedbefore the second control signal is generated.
 17. The method of claim12, further comprising: obtaining an indication of an ambienttemperature; obtaining an indication of a current temperature of a fluiddisposed within the tank; obtaining an indication of a desiredtemperature of the fluid disposed within the tank; obtaining a powerlevel value, based on the indication of the ambient temperature, theindication of the current temperature of the fluid, and the indicationof the desired temperature of the fluid; generating a control signalbased on the first power level value; and providing the control signalto the motor.
 18. The method of claim 14, further comprising: generatingheat within the tank before providing the first control signal to themotor.
 19. The method of claim 12, further comprising: providing a firstvalve adjacent to an inlet of the conduit; enabling air moved by thefluid propulsion device to flow through the first valve into theconduit; preventing air within the conduit from flowing through thefirst valve out of the conduit.
 20. The method of claim 18, furthercomprising: providing a second valve adjacent to an outlet of theconduit; enabling the air within the conduit to flow through the secondvalve out of the conduit; and preventing air outside of the conduit fromflowing through the second valve into the conduit.